The modern or low-wheeled harness racing sulky, has been used in this sport for more than eighty years. Due to their use of spoked wheels, sulkies have often been referred to as "bikes".
The conventional modern sulky essentially consists of a lightweight frame to which a pair of fixed wheels are mounted. The seat is normally mounted to the frame slightly behind the wheels at a level approximately even with the top of the wheels. Most sulkies are about five feet wide, measure between twenty five to thirty-two inches to the seat and weigh about forty pounds.
A major disadvantage of the prior art racing sulky is its susceptibility to tipping. These lightweight vehicles are drawn about an oval race course by specially trained horses at speeds in excess of 30 miles per hour. In the course of a race, maneuvering for position and unexpected traffic developments may cause even the best trained horse to mis-step or veer suddenly to one side. With conventional fixed wheel sulkies such sudden lateral movements by the horse have often produced serious accidents. The prior art sulky, due to its fixed position wheels, exhibits a resistance to sudden lateral movements, the wheel on the side of movement digs into the track and translates the lateral movement of the sulky into a vertical tipping force. Sometimes the trailing wheel merely leaves the ground momentarily; however often this results in a spill.
A second disadvantage of the prior art sulky is also related to its resistance to lateral movement. Since the sulky is harnessed directly to the horse it reacts to, or attempts to follow, the movement of the horse. The resistance to lateral movement mentioned above is thought to slow the prior art sulky. With each step, the horse's rolling gait is transmitted to the sulky in the form of a succession of alternating sidewise displacement forces. These sidewise forces are resisted by the fixedly mounted wheels
This clashing of the horse's movement and sulky's resistance has two potential detrimental effects. First, the effect of sidewise force may slow rotation of the wheels through increased friction with the track. Second and more importantly, this resistance restricts the rolling movement of the horse's gait and may thus slow the horse's pace.
Another disadvantage of the fixed-wheel sulky is its resistance to turning. On an oval track a good amount of the circuit consists of turning movements. The fixed wheel sulky resists the turn and produces torsional stresses on the harness shafts which restrict the horse's movements and may also result in a tipping action.
U.S. Pat. No. 3,847,408 discloses a single shaft fixed wheel sulky which realizes the advantage of eliminating some of these interferences with the horse's movements. Indeed, this sulky was reported to produce up to five second improvement in a horse's time over other fixed wheel sulkies. However, since this design permitted the horse to nearly turn around in its harness, it proved to be too dangerous and the regulations were changed to prohibit its use.
The search has continued for an improved sulky which will reduce the risk of tipping and produce improved performance.